Petri dishes, filled with agar-agar or other culture growth medium, are employed in vast numbers in many types of testing and research laboratories, and various types of apparatus have been proposed heretofore for the mass production of such filled dishes. In general, the rate of feed of growth medium in such apparatus must be restricted in order to prevent spillage from the dishes, and therefore the prior apparatus require either the intermittent stopping of each dish while it is filled with medium, or the speed of movement of the dishes is restricted to allow proper filling. Typical of such apparatus are those described in U.S. Pat. Nos. 3,050,915; 3,513,621; 3,719,023; and 4,170,861. In both types of apparatus the rate of production of filled dishes is limited, resulting in correspondingly high production cost.